On Mon, May 20, 2019 at 12:52:47PM +0900, Minchan Kim wrote: > - Approach > > The approach we chose was to use a new interface to allow userspace to > proactively reclaim entire processes by leveraging platform information. > This allowed us to bypass the inaccuracy of the kernel’s LRUs for pages > that are known to be cold from userspace and to avoid races with lmkd > by reclaiming apps as soon as they entered the cached state. Additionally, > it could provide many chances for platform to use much information to > optimize memory efficiency. > > IMHO we should spell it out that this patchset complements MADV_WONTNEED > and MADV_FREE by adding non-destructive ways to gain some free memory > space. MADV_COLD is similar to MADV_WONTNEED in a way that it hints the > kernel that memory region is not currently needed and should be reclaimed > immediately; MADV_COOL is similar to MADV_FREE in a way that it hints the > kernel that memory region is not currently needed and should be reclaimed > when memory pressure rises. I agree with this approach and the semantics. But these names are very vague and extremely easy to confuse since they're so similar. MADV_COLD could be a good name, but for deactivating pages, not reclaiming them - marking memory "cold" on the LRU for later reclaim. For the immediate reclaim one, I think there is a better option too: In virtual memory speak, putting a page into secondary storage (or ensuring it's already there), and then freeing its in-memory copy, is called "paging out". And that's what this flag is supposed to do. So how about MADV_PAGEOUT? With that, we'd have: MADV_FREE: Mark data invalid, free memory when needed MADV_DONTNEED: Mark data invalid, free memory immediately MADV_COLD: Data is not used for a while, free memory when needed MADV_PAGEOUT: Data is not used for a while, free memory immediately What do you think?
